Variable inductive coupling



Sept. 25, 1951 gHAMBERS 2,568,718

VARIABLE INDUCTIVE COUPLING Filed April 28, 1945 IE JAE-g. L

19. Ll 13 E.

AUDIO MULTIVIBRATCR H-F: 0S0.

AMPLIFIER POWER OUTPUT 5U P PLY Terrence H. Chambers Patented Sept. 25, 1951 UNITED STATES PATENT, OFFICE VARIABLE INDUCTIVE COUPLING Torrence H. Chambers, Washington, D. 0.

Application April 28, 1945, Serial No. 590,856

'2 Claims.

This invention relates to radio frequency oscillators or signal generators and, more particularly, to a test signal generator .especially designed to deliver any of three selected types of radio .frequency output, viz., a fifty percent square-wave modulation or vaseries of rapidly attenuated R.-F. pulses or an unmodulated (CW). The principal use of the signal generator of the present invention is as a generator of synthetic interference signals for use in the training of personnel .in the operation of ultra-high frequency radio equipment, particularly receivers, but oscillators or signal generators of this type also are useful in producing modulated or pulsed radio frequency voltages of predetermined magnitude for use in checking receiverequipment and similar work where frequencies of extreme accuracy are :not required.

One object of the present invention is to provide a radio frequency oscillator or signal generator including a novel attenuator arrangement for controlling the output voltage.

Another object of this invention is to provide a radio frequency oscillator or signal generator of the foregoing character which is of compact, rugged construction and completely self-contained in asingle, readily-portable carrying case.

Another object of .the invention is the provision of a signal generator having output characteristics such that it can be used either in the laboratory or in the .field as a source of variable radio frequency voltages, approximately calibrated, for checking the operation and overall perforance of :high frequency radio receivers.

A further object of the invention is the provision of a signal generator having output characteristics such that it can be used in the laboratory or in the field as a source of desired radio frequency test signals to simulate interference for purposes of training personnel in the operation of high frequency radio equipment.

A .still further object of the .invention is to proyide a test signal generator of the type described which .is of simple construction employing a mini- ;mum of components and without use of complicated or expensive circuits.

A feature of the invention is the arrangement and the novel method of attenuation for providing a variable R.-F. output having a selected degree of attenuation for subsequent use by a receiver or otherhigh frequency device to be tested. In the illustrated embodiment, the attenuator includes a turnable .or revolvable member which comprises a coaxial line type swinging link member with terminal coupling loops at both end portions electrically connected together in a-series circuit and 'ang-ularly disposed for simultaneously adjustable electromagnetic coupling relationship with a pair of fixed coupling loops. One of the fixed loops just mentioned is part of a coaxial line output line from the tuned circuit of the R.-F. oscillator and the other fixed coupling loop is characterized in that it forms an externally disposed extension of the inner conductor of the attenuator output line at an intermediate portion thereof. Means are provided for adjusting the swinging link to vary the inductive coupling relationship simultaneously between the associated loops and the fixed coupling loops to control the output voltage of the attenuator system.

A further feature of the invention is the arrangement and the novel methodof coupling into a coaxial line by use of a loop formed of a portion of the inner conductor which has been pulled out o through a side opening in the outer conductor of said line.

Other objects, features and advantages .of the invention will be apparent from the following detailed description of a preferred embodiment thereof taken in connection with the accompanying drawing, in which:

Fig. 1 .shows block schematic diagram form the several units included in a test signal generator arranged in accordance with the present invention;

.Fig. 2 is a diagrammatic representation showing the mounting of the swingable coaxial link coupling whereby swinging movement thereof is attained about the coaxial line per so as anaxis.

Referring more particularly to Fig. 1 the test signal generator comprises a multivibrator ID, a audio amplifier stage I I, a high frequency oscillator 12, an adjustable output attenuator l3 and a power-supplysource 4.-

The multivibrator 10 comprises a twin-.triode, heater-cathode type tube arranged in .a conventional symmetrical multivibrator circuit consisting of a two stage resistancecapacity coupled vacuum tube amplifier in which the output of each stage is coupled .to the input of the other stage. The coupling means for the multivibrator i0 includes a plurality of resistance-capacity combinations selectively coupled between the inputs and outputs of the stages to render the multivibrator l0 capable of operating to a plurality of selected frequencies.

The output of the multivibrator I is fed through a coupling capacitor to the control grid of a power amplifier tube. The power amplifier tube is of a pentode type having a cathode, a screen grid, a suppressor grid, a control grid, and a plate. The foregoing elements are connected in a conventional manner to operate the power amplifier tube as an audio amplifier l l in a manner well understood by those skilled in the art.

The oscillator [2 comprises a high frequency vacuum tube oscillator which may be of the Hartley type and having a tunable oscillatory circuit which includes an inductance and a variable capacitor associated therewith. The frequency of the oscillator I2 is controlled over the entire frequency band by adjustment of the variable capacitor in accordance with an approximately calibrated frequency scale on the control panel (not shown).

In the construction of the signal generator, as has been previously stated above, it is intended that three types of output shall be delivered, viz., fifty percent square-wave modulated or a series of rapidly attenuated R.-F. pulses or an unmodulated CW. To this end, switching devices 40 and ll are provided to permit selection of either square-wave modulation or pulse operation of the oscillator.

The output attenuator 13 comprises a coaxial line having at one end a loo (which may be a single turn loop or a plurality of turns) this loo taking a small portion of the R. F. voltage develo ed across the oscillator tuned circuit and transferring it by inductive coupling to the end loop 52 of the swingable link coupling 53. The link cou ling 53 is a substantially U-shaped coaxial line (see Fig. 2) having arms 54 and 55, the loop 52 terminating the end of arm 54 while at the end of arm 55 is a terminal loop 56 which transfers this energy by inductive cou ling to a loo 51. the latter 1000 being part of the inner conductor of a coaxial line 58 and rojecting outside thereof through an aperture 59 in the outer co ductor of said line at an intermediate po nt thereof. In Fig. 2 there is shown diagrammatically the general arrangement of the attenuator l3 wherein the coaxial link coupling 53 is supported so as to be swingable about an intermediate portion of itself as an axis, by means of a sleeve 60, to simultaneously adiust and control the inductive coupling between the pairs of loops 5|, 52 and 56, 51. Suitable gearing mechanism, such as gears El and 62, is provided operable by means of a knob 63 in conjunction with an approximately calibrated scale on the control panel to adjust the attenuator and consequently to control the supply of output R. F. energy from the osc llator l2 to the radio receiver under test (not shown) through suitable transmission lines (not shown) placed in series with the loop 51 and connected by means of suitable connections to the terminals of the coaxial line 58, the performance of this radio receiver in turn being observable in conventional manner on the screen of a cathode ray tube.

In accordance with the circuit arrangement of this invention as described above it will be seen that by means of the switches 40 and 4| the R. F. output of the signal generator may be amplitudemodulated or pulse-modulated. The attenuator 13 provides a variable R. F. output which is approximately calibrated. Power is supplied from a conventional type of power supply I4 to the test signal generator. The power supply il includes an input transformer energized by a source of alternating current. The secondary winding of the transformer is connected to the plates of a duplex-diode. The rectified output is delivered from the filament of the duplex-diode in a manner well understood by those skilled in the art.

Important advantages of this improved attenuation and coupling system are that no sliding contacts are required at the attenuator device and that both input and output coupling members thereof are fixedly positioned mechanically.

From the above, it should be seen that the invention provides a novel arrangement and method of transferring and attenuating the flow of high frequency oscillatory energy from an input element to an output element one or both of which elements being a coaxial line and both of said elements being fixed at spaced locations from each other with the output element connected to draw off the attenuated energy and the input element excited with high frequency oscillatory energy. By adjusting the relative coupling between the input and the output elements and an intermediate energy transfer link circuit the high frequency energy transfer to the output element is controlled and attenuated to the desired extent.

Although only one embodiment of the present invention has been disclosed and described herein it is to be expressly understood that various changes and substitutions may be made therein without department from the spirit of the invention as well understood by those skilled in the art. Reference, therefore, will be had to the appended claims for a definition of the limits of the invention.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. In combination with a generator for producing radio frequency energy, a voltage attenuator comprising input and output means, said input means comprisin a coaxial line energized by said radio frequency energy and terminated in a fixed loop, said output means comprising a coaxial line having an aperture in the outer conductor thereof and a fixed loop comprising a portion of the inner conductor thereof extending outwardly through said aperture beyond said outer conductor, a coaxial line link member having the ends thereof terminated in loops, one loop of said link member inductively coupled to said input means loop and the other loop thereof inductively coupled to said output loop means and means for moving said link member to vary the inductive coupling between said inductively coupled loops.

2. In combination, an input means comprising a coaxial line terminated in a fixed loop, an output means comprising a coaxial line having inner and outer conductors and a fixed loop comprising a portion of the inner conductor extending through said outer conductor intermediate the ends of the latter, a coaxial line link member having the ends thereof terminated in loops, one loop of said link member inductively coupled to said input loop and the other loop thereof inductively coupled to said output loop, and means for rotating said link member to vary the inductive coupling between said inductively coupled loops.

TORRENCE H. CHAMBERS.

(References on following page) 5 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Schaper Aug. 11, 1936 Chaffee Jan. '7, 1941 Reeves 1 Dec. 16, 1941 Milinowski Mar. 17, 1942 Lindquist Sept. 15, 1942 Tinus Oct. 6, 1942 Higgins Feb. 9, 1943 Number 6 Name Date Clifiord Feb. 16, 1943 Curtis Mar. 2, 1943 Dodington Aug. 28, 1945 Mouromtsefi Nov. 10, 1945 Archenbronn Dec. 11, 1945 Clapp Oct. 15, 1946 Ghosh Dec. 10, 1946 Edson Jan. 21, 1947 Folland Sept. 9, 1947 Harrison June 29, 1948 Goldstine June 29, 1948 Jacob July 26, 1949 

